Mark,
I went to my garage and I took the head off the Burke and I disassembled it so I could get the best possible measurements.
I made a template of cardboard with some of the measurements, I have also included some more photos of the base separated and
laid out for you to glee some more info before you start cutting the cast iron.
#1 The center to center measurement from the 2" TOP hole to the center of the LOWER hole is 4.316 measured from the template very close to 4 3/8
#2 The distance from the center of the LOWER hole to the center of the slot is 1.780.
I am not sure if all these back plates are the same as its a pretty good chunk of cast iron some of the measurements may be off a little, If I may
suggest it may benefit you to make a drawing or template based on the photos and sizes i have given you here to be sure it all lines up before
you start cutting. If you are interested in the template I made I can mail it to you. Let me know
I can't seem to upload photos every one i try I get ERROR uploading your file. look below they finally posted. alot of the photos would help a lot.
Regards
Wally Gehricke
dgehricke